Mammalian spermatozoa are vulnerable to spontaneous lipid peroxidation by 02, which appears to limit their lifespan in the oviduct. Work carried out during the present grant showed that peroxidation of rabbit and mouse sperm, as measured by malonaldehyde (MA), correlates closely with loss of motility and inactivation of superoxide dismutase (SOD). Sperm from both species produce 02 radical and H202; the latter arises from the former by the activity of SOD. Studies underway indicate that human sperm are similar to rabbit and mouse sperm in all these respects. Preliminary determinations of phospholipids in rabbit and mouse sperm show that most of the phosphatidylethanolamine and half the phosphatidylcholine is plasmalogen and that the plasmalogen component is preferentially lost in the course of lipid peroxidation. The specific aims of this proposal are: a. To measure the disappearance of plasmalogen from the phospholipid component of sperm from rabbit, mouse, and human during peroxidation; to correlate this loss with 02 radical production, loss of motility and membrane damage. The working hypothesis is that plasmalogens preferentially react with 02 radical and, by so doing, act as protectants for other phospholipids. b. To correlate the rate of peroxidation with the metabolic state of the cell, using rabbit sperm whose metabolism has been extensively characterized in this laboratory. The working hypothesis is that energy-depleted cells will be more sensitive to lipid peroxidation than fully energized cells. c. To test the correlation between intial SOD activity and sperm lifetime of individual samples of rabbit and human sperm, using samples obtained sequentially. The working hypothesis is that low SOD activity will predict short sperm lifetime. Dual wavelength spectrophotometry is used to quantitate production rates of H202, 02 radical and MA, and the steady state level of lipid hydroperoxide. Thin layer chromatography is used to determine diacyl-, lyso-, and plasmalogen-phospholipids and to determine the degree of unsaturation in the long chain acyl or alkylvinylether groups. The long range goal of this research is to clarify the mechanisms underlying spontaneous lipid peroxidation in mammalian sperm and thereby to understand what limits the viability of normal sperm in the presence of 02 and to apply this knowledge to the problem of unexplained male infertility in humans.